No group has claimed the four activists' abduction and they have not been heard from since.
Ankara-backed rebels played a key role in supporting Sharaa's Islamist group Hayat Tahrir al-Sham (HTS), which headed a rebel alliance that seized Damascus on December 8, toppling longtime ruler Bashar al-Assad.
The seismic change in Syria is expected to yield deeper Turkish sway just as a change of US administration is raising questions over how long Washington will keep backing the country's Kurdish-led forces.
Assad fled Syria following a lightning offensive spearheaded by the Islamist Hayat Tahrir al-Sham (HTS), more than 13 years after his crackdown on democracy protests precipitated one of the deadliest wars of the century.
Darwish was detained for months by one of the most feared branches of the former government's many-tentacled intelligence services.
Syrians will not miss Assad, a brutal ruler who failed his people.
The offensive, which took just 10 days to sweep across Syria and take the capital Damascus, stunned the world and brought an end to more than a half a century of brutal rule by the Assad clan.
"We would like to see the situation in the country stabilised somehow as soon as possible," Kremlin spokesman Dmitry Peskov told reporters.
"Their human capital, their experience will allow the country to flourish," Bashir said in an interview published Wednesday.
The Islamic State group fired chemical weapons against Kurdish forces in Syria and Iraq last month, Kurdish fighters and weapons experts have said reports The Economic Times.
A man - who joined Islamic State in Syria with 11 other family members of his family - is being held against his will after being "tricked" into going, his son tells British TV channel.
The US-led coalition fighting the Islamic State group is "intensifying" its campaign in northern Syria, President Barack Obama says.
British bank HSBC fires six staff after they filmed a mock Islamic State-style execution video during a team-building day out and posted footage online.
A video apparently released by the Islamic State group shows 25 men being shot dead in the ancient city of Palmyra, in Syria.
At least 25 members of Syria's al-Qaeda affiliate, al-Nusra Front, including a leader, are killed in a blast at a mosque in north-western Idlib province, activists say.
A senior member of the Islamic State (IS) group has been killed in an American drone strike in Syria last month, according to the US military.
A Bangladeshi family of 12 from England, including a baby and two grandparents, could have travelled to Syria after going missing, police have said.
A senior US commander in Afghanistan says that fighters allied with Islamic State are in contact with militants' Syrian headquarters.
The UN's cultural agency says destruction of antiquities and heritage sites in conflict zones by Islamic State and other extremist groups could amount to war crimes.
